Sharp R-7N76(B)M Скачать руководство пользователя страница 27

Страница: 27 / 49

R-7N76(W)M
R-7N76(B)M

unit is put in the Sensor Cooking mode.
As the sensor cooking proceeds, the food is heated to
generate moisture by which the resistance balance of
the bridge circuit is deviated to increase the voltage
available at AN6 terminal of the LSI. Then the LSI
observes that voltage at AN6 terminal and compares it
with its initial value, and when the comparison rate
reaches the preset value (fixed for each menu to be
cooked), the LSI causes the unit to stop sensor cooking;
thereafter, the unit get in the next necessary operation
automatically.
When the LSI starts to detect the initial voltage at AN6
terminal 16 seconds after the unit has been put in the
Sensor Cooking mode, if it is impossible to take a
balance of the bridge circuit due to disconnection of the
absolute humidity sensor, ERROR will appear on the
display and the cooking is stopped.

Absolute humidity sensor circuit

ABSOLUTE HUMIDITY SENSOR CIRCUIT

(1) Structure of Absolute Humidity Sensor

The absolute humidity sensor includes two thermistors
as shown in the illustration. One thermistor is housed
in the closed vessel filled with dry air while another is
in the open vessel. Each sensor is provided with the
protective cover made of metal mesh to be protected
from the external airflow.

(2) Operational Principle of Absolute Humidity Sensor

The figure below shows the basic structure of an
absolute humidity sensor. A bridge circuit is formed by
two thermistors and two resistors (R1 and R2).
The output of the bridge circuit is to be amplified by the
operational amplifier.
Each thermistor is supplied with a current to keep itself
heated at about 150˚C and the resultant heat is
dissipated in the air and if the two thermistors are
placed in different humidity conditions they show
different degrees of heat conductivity leading to a
potential difference between them causing an output
voltage from the bridge circuit, the intensity of which is
increased as the absolute humidity of the air increases.
Since the output is very minute, it will be amplified by
the operational amplifier.

(3) Detector Circuit of Absolute Humidity Sensor

This detector circuit is used to detect the output voltage
of the absolute humidity circuit to allow the LSI to
control sensor cooking of the unit.
When the unit is set in the sensor cooking mode, 16
seconds later the detector circuit starts to function and
the LSI observes the initial voltage available at its AN6
terminal. With this voltage given, the switches SW1 to
SW5 in the LSI are turned on in such a way as to
change the resistance values in parallel with R-1.
Changing the resistance values results in that there is
the same potential at both F-3 terminal of the absolute
humidity sensor and AN7 terminal of the LSI. The
voltage of AN6 terminal will indicate about -2.5V. This
initial balancing is set up about 16 seconds after the

Sensing part
(Open vessel)

Sensing part
(Closed vessel)

Operational
amplifier

Output
voltage

S : Thermistor
open vessel

C : Thermistor
closed vessel

Absolute humidity (g/m )

Output voltage

Absolute humidity vs,
output voltage characterist

SW1

SW2

SW4